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        <p>JAVAScript闭包:在函数内部定义一个函数,并且该函数引用到了当前作用域中的变量,并将该函数返回.</p>
<h2 id="创建一个闭包"><a href="#创建一个闭包" class="headerlink" title="创建一个闭包"></a>创建一个闭包</h2><p>闭包是指有权访问另一个函数作用域中的变量的函数。创建闭包的常见方式,就是在一个函数内部创建另一个函数。</p>
<p>实例:</p>
<figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE html&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">title</span>&gt;</span>bibao<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line"></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">type</span>=<span class="string">"text/javascript"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="actionscript">      <span class="function"><span class="keyword">function</span> <span class="title">fun1</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">var</span> a = <span class="number">1</span>;</span></span><br><span class="line"><span class="actionscript">        <span class="function"><span class="keyword">function</span> <span class="title">fun2</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="javascript">          <span class="built_in">console</span>.log(a);</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">return</span> fun2;</span></span><br><span class="line"><span class="undefined">      &#125;</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> result = fun1();</span></span><br><span class="line"><span class="actionscript">      result()<span class="comment">//result()可以访问其他函数作用域中的变量,result()就是闭包.</span></span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h2 id="闭包的特点"><a href="#闭包的特点" class="headerlink" title="闭包的特点"></a>闭包的特点</h2><p>优点:</p>
<ul>
<li>实现变量的私有化,减少全局变量的定义.</li>
<li>动态生成数据(根据参数变化).</li>
</ul>
<p>缺点:</p>
<ul>
<li>闭包变量常驻内存,增加内存消耗.</li>
</ul>
<h2 id="实例"><a href="#实例" class="headerlink" title="实例"></a>实例</h2><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">&lt;!DOCTYPE html&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"utf-8"</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">title</span>&gt;</span>count<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">    <span class="tag">&lt;<span class="name">script</span> <span class="attr">type</span>=<span class="string">"text/javascript"</span>&gt;</span><span class="undefined"></span></span><br><span class="line"><span class="actionscript">      <span class="function"><span class="keyword">function</span> <span class="title">count</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">var</span> count = <span class="number">50</span>;</span></span><br><span class="line"><span class="actionscript">        <span class="function"><span class="keyword">function</span> <span class="title">add</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="undefined">          count++;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="actionscript">        <span class="function"><span class="keyword">function</span> <span class="title">red</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="undefined">          count--;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="actionscript">        <span class="function"><span class="keyword">function</span> <span class="title">get</span><span class="params">()</span></span>&#123;</span></span><br><span class="line"><span class="actionscript">          <span class="keyword">return</span> count;</span></span><br><span class="line"><span class="undefined">        &#125;</span></span><br><span class="line"><span class="actionscript">        <span class="keyword">return</span> [add, red, <span class="keyword">get</span>];</span></span><br><span class="line"><span class="undefined">      &#125;</span></span><br><span class="line"><span class="undefined"></span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> stucount = count();</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> addstu = stucount[<span class="number">0</span>];</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> redstu = stucount[<span class="number">1</span>];</span></span><br><span class="line"><span class="actionscript">      <span class="keyword">var</span> getstu = stucount[<span class="number">2</span>];</span></span><br><span class="line"><span class="undefined">      addstu();</span></span><br><span class="line"><span class="undefined">      addstu();</span></span><br><span class="line"><span class="undefined">      redstu();</span></span><br><span class="line"><span class="javascript">      <span class="built_in">console</span>.log(getstu());</span></span><br><span class="line"><span class="actionscript">      <span class="comment">//count无法直接修改,甚至访问不到,只能通过3个闭包函数进行操作.</span></span></span><br><span class="line"><span class="undefined">    </span><span class="tag">&lt;/<span class="name">script</span>&gt;</span></span><br><span class="line">  <span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
<h2 id="经典面试题"><a href="#经典面试题" class="headerlink" title="经典面试题"></a>经典面试题</h2><p>下面的题目是面向对象与闭包相结合.</p>
<figure class="highlight kotlin"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line">&lt;!DOCTYPE html&gt;</span><br><span class="line">&lt;html&gt;</span><br><span class="line">  &lt;head&gt;</span><br><span class="line">    &lt;meta charset=<span class="string">"utf-8"</span>&gt;</span><br><span class="line">    &lt;title&gt;closure&lt;/title&gt;</span><br><span class="line">  &lt;/head&gt;</span><br><span class="line">  &lt;body&gt;</span><br><span class="line">    &lt;script type=<span class="string">"text/javascript"</span>&gt;</span><br><span class="line">    function <span class="function"><span class="title">fun</span><span class="params">(n,o)</span></span> &#123;</span><br><span class="line">    console.log(o);</span><br><span class="line">        <span class="keyword">return</span> &#123;</span><br><span class="line">            <span class="function"><span class="keyword">fun</span>:<span class="title">function</span><span class="params">(m)</span></span> &#123;</span><br><span class="line">                <span class="keyword">return</span> <span class="function"><span class="title">fun</span><span class="params">(m,n)</span></span>;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;;</span><br><span class="line">      &#125;</span><br><span class="line">      <span class="keyword">var</span> a = <span class="function"><span class="title">fun</span><span class="params">(<span class="number">0</span>)</span></span>;</span><br><span class="line">      a.<span class="keyword">fun</span>(<span class="number">1</span>);<span class="comment">//0</span></span><br><span class="line">      a.<span class="keyword">fun</span>(<span class="number">2</span>);<span class="comment">//0</span></span><br><span class="line">      a.<span class="keyword">fun</span>(<span class="number">3</span>);<span class="comment">//0</span></span><br><span class="line">      <span class="keyword">var</span> b = <span class="function"><span class="title">fun</span><span class="params">(<span class="number">0</span>)</span></span>.<span class="keyword">fun</span>(<span class="number">1</span>).<span class="keyword">fun</span>(<span class="number">2</span>).<span class="keyword">fun</span>(<span class="number">3</span>);<span class="comment">//0 1 2</span></span><br><span class="line">      <span class="keyword">var</span> c = <span class="function"><span class="title">fun</span><span class="params">(<span class="number">0</span>)</span></span>.<span class="keyword">fun</span>(<span class="number">1</span>);<span class="comment">//0</span></span><br><span class="line">      c.<span class="keyword">fun</span>(<span class="number">2</span>);<span class="comment">//1</span></span><br><span class="line">      c.<span class="keyword">fun</span>(<span class="number">3</span>);<span class="comment">//1</span></span><br><span class="line"></span><br><span class="line">    &lt;/script&gt;</span><br><span class="line"></span><br><span class="line">  &lt;/body&gt;</span><br><span class="line">&lt;/html&gt;</span><br></pre></td></tr></table></figure>

      
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